LSD was a relative latecomer to long-established traditions of humans consuming hallucinogenic substances. But in a linguistic sense, it was the first psychedelic. In 1956, British psychiatrist Humphry Osmond coined the term “psychedelic” to describe LSD’s intoxicating effects in correspondence with writer Aldous Huxley. Those who ingest the drug can experience kaleidoscopic visual patterns, a temporary dissolution of self, a slowing or stopping of time, and wild shifts in mood that can range from deep euphoria to severe anxiety and confusion. “To fathom Hell or soar angelic, Just take a pinch of psychedelic,” Osmond quipped in his letter to Huxley.
Read more: “This Obscure 1960s Guide to LSD Holds Up”
Since at least 2012, scientists have believed that LSD and other psychedelics such as psilocybin alter experience by turning the dial down on activity in the brain’s specific control centers, such as the default mode network, which serves as a central conductor, regulating self-reflection and autobiographical memory and maintaining a sense of ego, or self. More recent research has complicated this idea somewhat, suggesting that connections between some networks are actually strengthened by psychedelics.
But now a small study published earlier this month proposes that LSD may also speed up some key brain rhythms and make brain activity more fractal, with certain patterns emerging and repeating across different timescales. Rather than quieting activity in certain control regions, the drug may also simply alter the background hum. In other words, it’s less that LSD turns off the brain’s controller than that it reshuffles how the whole system talks to itself. The team published their results in Communications Biology.
“Imagine a radio station switching its broadcast frequency from 99.5 to 100.5 FM,” said co-author Karim Jerbi, a Université de Montréal neuroscientist and researcher at Mila–the Quebec Artificial Intelligence Institute, in a statement. “If your radio stays tuned to 99.5, the signal may seem distorted or lost. In the same way, overlooking the shift to faster brain rhythms can lead us to misinterpret LSD’s effects on the brain.” The study was co-authored by Jerbi, together with his doctoral student Venkatesh Subramani and others.
Jerbi and his colleagues re-analyzed the brain recordings of 17 volunteers who either got LSD or a placebo saltwater injection on two separate days. To analyze the subjects’ brain rhythms, the researchers used a technique called magnetoencephalography (MEG), which picks up tiny magnetic fields the brain gives off and can measure changes in that activity over a matter of milliseconds. The volunteers lay quietly with their eyes closed, sometimes in silence and sometimes while listening to one of two seven-minute excerpts from the electro-acoustic ambient album Yearning by Robert Rich and Lisa Moskow.
The team found that LSD sped up the two main rhythms in the brain, known as alpha, which dominates when we’re at rest, and beta, which is linked to focus and decision-making. Using MEG, the researchers found that, in fact, alpha waves sped up by about 2 beats per second, and beta by about 5 beats per second, across large swaths of the cerebral cortex. Older studies had not picked up this change in rhythm because of the way they measured brain activity.
The old method measured only strength: how much total power fell within a specific pre-determined band of frequencies that typically correspond with each type of wave. For instance, in a healthy resting person, alpha waves typically peak pretty regularly at around 10 beats per second—though the exact number varies slightly from one person to the next. The new method separated each rhythm from background static and measured both how fast the frequency was moving, and how strong it was at the peak.
Jerbi and his colleagues also found that the so-called background “hum” of the brain, in which slower frequencies are naturally louder than fast ones, got flatter: Activity became more evenly spread out across speeds, resulting in a less organized signal. But the brain’s overall activity got more complex, more fractal, and less predictable, as measured by the number of distinct patterns showing up in the signal and how many variations occurred in the signal across time. These fractal patterns are found across nature, and echo the kinds of visual patterning that many people taking the drug experience, in which tiny patterns nest one within another like the geometries of a snowflake.
The fact that fractal patterns were found in the brain signal does not necessarily imply a direct link to fractal changes in vision, said Jerbi. “Our findings lend support to this intriguing hypothesis, but they do not yet confirm it. We measure the fractal structure of brain signals over time, not the fractal structure of the images people perceive.”
The brain activity patterns observed by the researchers were clustered in areas associated with vision, hearing, language, emotion, and imagery, but mostly did not affect regions associated with movement, which is consistent with how the drug changes experience. When a person takes LSD, perception is scrambled, but the basic machinery of movement typically remains intact.
One finding surprised the team: Listening to music did not boost the effects of the drug. If anything the data suggested that in fact, music dampened the effects of LSD: The background hum became more dynamic in the participants listening to music, and complexity declined. One hypothesis the scientists offered is that music can act as an anchor, keeping the brain more organized. But this result didn’t hold up under strict statistical analysis, so it’s more of a hint than a fact.
The patterns the team found seemed to be consistent enough that they could be recognized by AI. They trained a machine learning model to predict which brain recordings came from participants on LSD and which ones were from volunteers given a placebo. The model did reasonably well, with between 68 percent and 82 percent accuracy, depending on the specific feature, such as rhythm scores, background hum activity, and complexity scores.
The authors noted that there are some limits to the findings. The study only looked at 17 people, and the recordings came from an older dataset, re-analyzed with the newer methods. The high-frequency gamma findings could also reflect the fact that muscle twitches can sometimes fake certain brain signals, but the authors say the patterns they found are likely too organized for that.
But if the findings hold up, they suggest that the experience of taking LSD is even more complex than we had previously appreciated, and ultimately that it may change our brains in ways that are directly reflected in perceptual experience. 
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